Apparatus, system and method enabling multiplexed arrangement of optical fiber for sensing of operating conditions within a structural member

ABSTRACT

Embodiments of the present invention provide a unique new approach to generating operating condition information used for assessing flow assurance and structural integrity. More specifically, apparatuses, systems and methods configured in accordance with embodiments of the present invention enable multiplexed arrangement of optical fiber for sensing of operating conditions within a structural member and utilize fiber optic sensors for enabling monitoring of operating condition information within one or more elongated tubular members. To this end, fiber optic sensors are strategically placed at a plurality of locations along a length of each elongated tubular member thereby allowing critical operating conditions such as strain, temperature and pressure of the elongated tubular member and/or a fluid therein to be monitored. A multiplexing unit is used for allowing selective configuration of individual lengths of optical fiber for creating one or more contiguous optical fiber structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This continuation-in-part patent application claims priority fromco-pending United States non-provisional patent application having Ser.No. 13/852,896, filed 23 Mar. 2013, entitled “AN APPARATUS TO MONITORFLOW ASSURANCE PROPERTIES IN CONDUITS”, having a common applicantherewith and being incorporated herein in its entirety by reference.

United States non-provisional patent application having Ser. No.13/852,896 is a continuation of and claims priority from co-pendingUnited States non-provisional patent application having Ser. No.12/882,993 filed 15 Sep. 2010, entitled “APPARATUS TO MONITOR FLOWASSURANCE PROPERTIES IN CONDUITS”, having a common applicant therewithand being incorporated herein in its entirety by reference.

United States non-provisional patent application having Ser. No.12/882,993, claims priority from co-pending United States provisionalpatent application having Ser. No. 61/242,746, filed 15 Sep. 2009,entitled “APPARATUS TO MONITOR FLOW ASSURANCE PROPERTIES IN CONDUITS”,having a common applicant therewith and being incorporated herein in itsentirety by reference.

FIELD OF THE DISCLOSURE

The disclosures made herein relate generally to monitoring of operatingconditions within structural members and, more particularly, toapparatuses, systems and methods enabling multiplexed arrangement ofoptical fiber for sensing of operating conditions within a structuralmember.

BACKGROUND

Structural members for which it is necessary to monitor operatingcondition information thereof are well-known and are used in manyindustries and applications. Such structural members can have a solidcross sectional construction or have an interior space. An elongatedtubular member (e.g., a pipe) is an example of such a structural memberwith an interior space. Elongated tubular members used in offshoredrilling and production systems in the oil and gas industry are a primeexample of structural members for which it is necessary to monitoroperating condition information thereof.

Offshore drilling and production systems include a work platform at asea surface (i.e., a surface work platform) that is in communicationwith a production field beneath the seafloor. A first type of conduit,which is generally referred to a riser, is required to support equipmentand materials being delivered from the surface work platform to thesubsea field, and/or a conduit for lifting oil and gas being producedfrom the subsea field to the surface work platform. A second type ofconduit, which his generally referred to as a pipeline, links wellheadsto a processing site. These conduits are examples of elongated tubularmembers.

Many pipelines are deployed in subsea environments where watertemperatures can cool the all or a portion of the pipeline that carriesthe hydrocarbon from the wellhead to the processing site. As hot gasesthat flow from the wellhead (i.e., particularly subsea wellheads) aresubjected to cooling, hydrates can precipitate from the product andresults in flow restrictions and in extreme cases can completely blockthe pipeline. In other instances, slow buildup of paraffin wax on theinterior of the pipeline can cause flow restrictions. These blockagesand flow restrictions pose significant risk to safe and efficientoperation of such pipelines.

Tension leg platforms, floating rigs, jack-up rigs and other knownoffshore drilling and production systems are examples of surface workplatforms. In many of these systems, in addition to the aforementionedtypes of conduits, some sort of legs or equivalent platform supportstructures extends from the sea floor to the surface work platform.These platform support structures generally have a tubular constructionand are, thus, another example of a tubular structural member.

A tension leg platform (TLP) is a specific example of a surface workplatform having conduits and platform support structures (i.e., tubularstructural members) for which operating conditions need to be monitored.A TLP, which is a permanently positioned structure used for theproduction of oil and gas in offshore environments, uses platformsupport structures in the form of tension legs (i.e., also referred toas tendons) to support the platform above the sea surface. TLPs, whichare typically used in water depths ranging from 1000 to 5000 feet, aresecured in place using tension legs that each have a first end attachedto a respective portion (e.g., corner) of a platform portion of the TLPand that have a second end that is attached to a respective piling thathas been driven into the sea floor. Tension legs of a TLP are typicallymade of tubular steel. In order for the TLP to work properly, thetension legs are kept under a relatively high level of tension. Suchimplementation of the tension legs restricts vertical motion of theplatform that would otherwise occur due to tides and wave action. Amajor advantage of TLPs is that the wellhead can be placed on thesurface rather than on the sea floor, thereby giving better access andsimpler production control.

In a typical TLP installation, three load sensors are installed into thetendon top connector assembly, which is on a sub-platform or bridge foreach tendon, below the primary work platform. The data from these loadsensors is then used to calculate the maximum, minimum and mean tensionsand standard deviation in the tendon, together with the bending movementangle. Historically, the load cells are unreliable and often fail earlyin their service life such as due to their exposure to seawater andother harsh environmental conditions.

Elongated tubular members such as tension legs, risers and pipelines aresubject to environmental conditions such as the flow, wave action andtemperature of the surrounding seawater. These environmental conditionseffect operating conditions such as, for example, tension, bending,compressive forces, expansion and contraction due to changes in watertemperature, internal pressure of fluids within the risers, and otheroperating conditions strains and stresses to which the elongated tubularmembers are subjected. To ensure safe and reliable operation of suchelongated tubular members, an operating condition monitoring system isrequired to provide reliable measurement of operating conditioninformation in each of the elongated tubular members and output suchoperating condition information, preferably in real-time. When themonitoring system fails, it is often necessary to shut down the drillingor production system at significant expense such has due to lost revenueand loss of drilling or production time

As is well-known, it is desirable to operate drilling and productionsystems in a safe, reliable, predictable and efficient manner. To thisend, it is beneficial to monitor operating condition information ofelongated tubular members of such drilling and production systems,whether offshore-based or land-based. Examples of operating conditioninclude, but are not limited to, strain within a wall of an elongatedtubular members, pressure within an interior space of the elongatedtubular members, torsion applied to the elongated tubular members,temperature of the wall or surface of the elongated tubular members,temperature of a fluid within the interior space of the elongatedtubular members, and flow confirmation of a fluid within the interiorspace of the elongated tubular members.

Various devices and systems have been deployed to generate and monitoroperating condition information. Examples of these devices and systemsinclude, but are not limited to, load cells on TLP tension legs,mechanical strain gauges on risers and pipelines, invasive sensors onrisers and pipelines (e.g., which penetrate the conduit), and othertypes of devices and systems. These types of prior art devices andsystems are of limited functional value in that they provide less thanoptimal operating condition information, are subject to early fatiguecaused by the rigorous environmental conditions in which they areemployed, and often undesirably require invasive installationtechniques.

Therefore, apparatuses, systems and sensor housing assemblies thatutilize fiber optic sensors for enabling monitoring of operatingcondition information within one or more elongated tubular members toovercome drawbacks associated with conventional approaches forgenerating and monitoring operating condition information would beadvantageous, desirable and useful.

SUMMARY OF THE DISCLOSURE

Embodiments of the present invention provide a unique approach togenerating operating condition information used for assessing flowassurance and structural integrity. More specifically, apparatuses,systems and sensor housing assemblies configured in accordance withembodiments of the present invention utilize fiber optic sensors forenabling monitoring of operating condition information within one ormore elongated tubular members. To this end, such fiber optic sensorscan be strategically placed at a plurality of locations along a lengthof each elongated tubular member thereby allowing critical operatingconditions such as strain, temperature and pressure of the elongatedtubular member and/or a fluid therein to be monitored.

Advantageously, embodiments of the present invention provide a simpleyet effective and reliable approach of monitoring operating conditionsalong elongated tubular members that can be on the order of 70 miles ormore. Furthermore, embodiments of the present invention advantageouslyallow for such fiber optic sensors to be installed before or afterdeployment of the elongated tubular members. In preferred embodiments,the fiber optic sensors are integrated into respective sensor housing,which allow a plurality of fiber optic sensors to the mounted on anelongated tubular member through mounting of the sensor housing thereon.Operating condition information from the fiber optic sensors of aplurality of sensor housings is communicated to a data acquisitionsystem through one or more optical fibers.

In one embodiment of the present invention, an apparatus for sensingoperating condition information from an elongated tubular membercomprises a plurality of tubular member interface bodies, a plurality ofoptical fibers, an optical sensing module, and a multiplexing unit. Eachone of the tubular member interface bodies includes a tubular memberengagement portion and an optical fiber engagement portion. Each one ofthe optical fibers has a first end and a second end. Two or more of theoptical fibers have at least one operating condition signal generatingportion between the first and second ends thereof. The at least oneoperating condition signal generating portion of the two or more of theoptical fibers is attached along a length of the optical fiberengagement portion of a respective one of the tubular member interfacebodies to thereby form a plurality of operating condition sensorsconnected to the elongated tubular member. The optical sensing modulehas at least one signaling port. The multiplexing unit includes aplurality of optical fiber interfaces each having a downstream facingport and an upstream facing port. The upstream facing port of each oneof the optical fiber interfaces is connectable to each other one of theupstream facing ports. Each end of each one of the optical fibers isoperably connected to the downstream facing port of a respective one ofthe optical fiber interfaces. The upstream facing ports are connected toeach other such that at least two of the optical fibers are connected toeach in a series fashion to form a contiguous optical fiber structurehaving opposing ends. The upstream facing port connected to an end ofthe contiguous optical fiber structure is connected to the at least onesignaling port of the optical sensing module for enabling sensor datagenerated within the contiguous optical fiber structure to be providedfrom the multiplexing unit to the optical sensing module.

In another embodiment of the present invention, a method of collectingoperating condition information from an elongated tubular membercomprises a plurality of operations. An operation is performed formonitoring an operating condition signal provided at one of opposingends of a contiguous optical fiber structure to determine operatingcondition information generated by a plurality of operating conditionsensors connected to the elongated tubular member. The contiguousoptical fiber structure comprises a plurality of individual lengths ofoptical fiber connected in an end-to-end fashion to form a single lengthof optical fiber having the opposing ends. At least two of theindividual lengths of optical fiber includes at least one of theoperating condition sensors integral therewith between opposing endsthereof. An operation is performed for detecting, via the operatingcondition signal, loss of operating condition information correspondingto at least one of the individual lengths of optical fiber. In responseto detecting the loss of operating condition information, an operationis performed for reconfiguring monitoring of the operating conditionsignal. Reconfiguring such monitoring includes one of causing anoperating condition signal to be provided at both of the opposing endsof the contiguous optical fiber structure and monitoring a respectiveoperating condition signal at both of the ends of the contiguous opticalfiber structure and excluding the at least one of the individual lengthsof optical fiber from within the contiguous optical fiber structure tocreate a reconfigured version of the contiguous optical fiber structureand continuing to monitor the operating condition signal provided at theone of the opposing ends of the contiguous optical fiber structure.

In another embodiment of the present invention, a system comprises aplurality of operating condition sensors, an optical sensing module, anda multiplexing unit. The operating condition sensors are connected to anelongated tubular member. Each one of the operating condition sensorsincludes a plurality of an operating condition signal generating portionof a respective one of a plurality of optical fibers each having a firstend and a second end. The optical sensing module has at least onesignaling port. The multiplexing unit includes a plurality of opticalfiber interfaces each having a downstream facing port and an upstreamfacing port. The upstream facing port of each one of the optical fiberinterfaces is connectable to each other one of the upstream facingports. Each end of each one of the optical fibers is operably connectedto the downstream facing port of a respective one of the optical fiberinterfaces. The upstream facing ports are connected to each other suchthat at least two of the optical fibers are connected to each in aseries fashion to form a contiguous optical fiber structure havingopposing ends. The upstream facing port connected to an end of thecontiguous optical fiber structure is connected to the at least onesignaling port of the optical sensing module for enabling sensor datagenerated within the contiguous optical fiber structure to be providedfrom the multiplexing unit to the optical sensing module.

These and other objects, embodiments, advantages and/or distinctions ofthe present invention will become readily apparent upon further reviewof the following specification, associated drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view showing an operating condition monitoringapparatus configured in accordance with an embodiment of the presentinvention.

FIG. 2 is a perspective view of a sensor housing assembly configured inaccordance with an embodiment of the present invention.

FIG. 3 is a fragmentary cross-sectional view taken along the line 3-3 inFIG. 2 .

FIG. 4 is a fragmentary cross-sectional view taken along the line 4-4 inFIG. 2 .

FIG. 5 is a cross-sectional end view of a fiber optic sensor configuredin accordance with an embodiment of the present invention.

FIG. 6 is a cross-sectional side view of a temperature-indicating fiberoptic sensor configured in accordance with an embodiment of the presentinvention.

FIG. 7 is a diagrammatic view showing a detected signal in accordancewith wavelength division multiplexing for a plurality of fiber opticsensors.

FIG. 8 is a fragmentary cross-sectional view showing a fiberoptic cableconfigured in accordance with an embodiment of the present invention.

FIG. 9 is a side view showing a length of unjacketed optical fiberextending over an exterior surface of an elongated tubular member andcovered by a layer of protective material.

FIG. 10 is a multi-tubular member operating condition monitoringapparatus configured in accordance with an embodiment of the presentinvention.

FIG. 11 is a diagrammatic view showing a multiplexing unit providing forsignaling via a first end of a contiguous optical fiber structure.

FIG. 12 is a diagrammatic view showing the multiplexing unit of FIG. 11providing for signaling via both first and second ends of the contiguousoptical fiber structure when a discontinuity is detected therein.

FIG. 13 is a diagrammatic view showing the multiplexing unit of FIG. 11providing for reconfiguration of constituent lengths of optical fiber ofthe contiguous optical fiber structure when a discontinuity is detectedtherein.

FIG. 14 is a perspective view of a typical pipeline, before deploymentin a subsea environment.

FIG. 15 is a side view showing fiber optic sensors as applied to theexterior wall of the pipeline.

FIG. 16 is a side view showing a collector for collecting the data froma plurality of sensors attached to the pipeline.

FIG. 17 is a perspective view showing an alternative collector forcollecting the data from a plurality of sensors attached to thepipeline.

DETAILED DESCRIPTION

FIG. 1 shows an apparatus 100 configured in accordance with anembodiment of the present invention. The apparatus 100 includes anelongated tubular member 102 that is connected to a support structure104. A plurality of sensor housing assemblies 106 a-106 n are mounted ina spaced-apart arrangement along a length of the elongated tubularmember 102. The sensor housing assemblies 106 a-106 n are connected toeach other and to an optical sensing module 107, such as at a signalingport thereof, by a fiberoptic cable 108.

The sensor housing assemblies 106 a-106 n, the optical sensing module107 and the fiberoptic cable 108 jointly provide for operating conditioninformation for the elongated tubular member 102, a fluid within theelongated tubular member 102, or both to be generated, communicated andmonitored. As discussed below in greater detail, each one of the sensorhousing assemblies 106 a-106 n includes one or more fiber optic sensors(not specifically shown in FIG. 1 ) that are configured for generatingspecific respective operating condition information. Examples of suchoperating condition information includes, but is not limited to, strainwithin a wall of the elongated tubular member 102, pressure within aninterior space of the elongated tubular member 102, torsion applied tothe elongated tubular member 102, temperature of the wall or surface ofthe elongated tubular member 102, temperature of a fluid within theinterior space of the elongated tubular member 102, and flowconfirmation of a fluid within the interior space of the elongatedtubular member 102.

Embodiments of the present invention are not limited to any particularelongated tubular member 102 or support structure 104. However, in manyapplications, a given elongated tubular member will typically be used inassociation with a corresponding support structure. For example, wherethe support structure is a tension leg platform (TLP), an elongatedtubular member thereof may be a tension leg or a riser. In anotherexample, where the support structure is a wellhead, an elongated tubularmember thereof may be a pipeline or the like.

Referring now to FIGS. 2 and 3 , specific aspects of the sensor housingassemblies 106 a-106 n are presented. As shown in FIG. 2 , each of thesensor housing assemblies 106 a-106 n may include one or morelongitudinal strain fiber optic sensors 110, one or more hoop strainfiber optic sensors 112, one or more torsional strain fiber opticsensors 114, and one or more temperature-sensing fiber optic sensors116. Preferably, a temperature-sensing fiber optic sensor used as atemperature compensation sensor is located in close proximity toassociated strain fiber optic sensors, but is isolated from the strainfield (e.g., as provided for by the tubular member interface body 118 ofthe temperature-sensing fiber optic sensor 116 discussed below inreference to FIG. 6 ).

In preferred embodiments, each one of the fiber optic sensors isintegrated into a sensor housing 117 of a respective one of the sensorhousing assemblies 106 a-106 n. Each one of the fiber optic sensors110-116 has a tubular member interface body 118 that is exposed at aninterface surface 119 of the sensor housing 117 that defines a centralpassage 120 thereof. An exterior surface of the elongated tubular memberis engaged with (e.g., bonded to) the tubular member interface body 118.A longitudinal axis of the central passage 120 extends approximatelyparallel with a longitudinal axis of the elongated tubular member 102.In preferred embodiments, four (4) longitudinal strain fiber opticsensors 110, which are preferably angularly spaced by 90 degrees aroundthe central passage 120 of the sensor housing 117, may be placed withinthe sensor housing 117 of a respective one of the sensor housingassemblies 106 a-106 n.

Preferably, the sensor housing 117 is a one-piece structure made from aresilient polymeric material. Examples of such a one-piece structureinclude, but are not limited to casting structures and moldedstructures. For allowing the elongated tubular member 102 to be disposedwithin the central passage 120 of the sensor housing 117, the sensorhousing 117 may include a slot 122 or other feature therein for allowingthe elongated tubular member 102 to be placed into the′ central passage120 and fixedly secured to the sensor housing 117. To this end, thesensor housing is preferably made in a manner (e.g., made from aresilient material) for enabling a width of the slot 122 orconfiguration of such other feature to be selectively manipulated (e.g.,increased by flexure of the sensor housing 117).

Referring to FIGS. 2-6 , the tubular member interface body 118 of eachone of the fiber optic sensors (110-116) has a tubular member engagementportion 124 that is exposed at the interface surface 119 of the sensorhousing 117 and an optical fiber engagement portion 126 that is withinthe sensor housing 117. This arrangement allows for the sensor housing117 and thus the tubular member interface bodies 118 thereof to beengaged with an exterior surface of the elongated tubular member 102. Inpreferred embodiments, the tubular member interface bodies 118 arebonded to the exterior surface of the elongated tubular member 102 byuse of a suitable bonding material. Such a suitable bonding material(e.g., a 2-part epoxy resin or the like) will enable temperature andstrain exhibited at the exterior surface of the elongated tubular member102 to be imparted upon the tubular member interface body(ies) 118thereof with negligible attenuation. Preferably, the tubular memberinterface bodies 118 are made from a metallic material that has acoefficient of thermal expansion that is substantially the same as acoefficient of thermal expansion of a material from which the elongatedtubular member 102 is made and have a thickness oat optimized requiredstructural integrity with respect to transmission of strain and/or heattransfer.

As best shown in FIGS. 2-5 , each tubular member interface body 118 usedfor providing strain-specific operating condition information (e.g., ofsensors 110-114) preferably has a length that is substantially greaterthan a width thereof, are orientated with the length direction extendingsubstantially parallel to the direction of the related strain, and havespaced-apart, substantially-parallel opposing major surfaces (i.e., thetubular member engagement portion 124 and the optical fiber engagementportion 126 each define a respective one of the spaced-apart opposingmajor surfaces). As best shown in FIG. 6 , the tubular member interfacebody 118 used for providing temperature-specific operating conditioninformation (e.g., of sensor 116) is L-shaped and has an end surface 128and side surface 130 that respectively defining an end face thereof anda side face thereof. The end surface 128 is the tubular memberengagement portion 124 and the side surface 130 is the optical fiberengagement portion 126.

As shown in FIGS. 3-6 , the optical fiber engagement portion 126 of eachtubular member interface body 118 is attached to an optical fiber 134 ofthe fiberoptic cable 108 at an operating condition signal generatingportion 132 thereof. Each tubular member interface body 118 and theattached operating condition signal generating portion 132 of theoptical fiber 134 jointly for a respective one of the fiber optic sensor(110-116). Attachment of the optical fiber 134 to the optical fiberengagement portion 126 of the tubular member interface body 118 incombination with the material selection and dimension of the tubularmember interface body 118 preferably provides for negligible attenuationof strain events (i.e., expansion-contraction) and thermal events (i.e.,temperature change) exhibited at the exterior surface of the elongatedtubular member being imparted upon the operating condition signalgenerating portion 132 of the strain-sensing fiber optic sensors110-114. To this end, in preferred embodiments, such attachment includesbonding with a suitable bonding material 135 (e.g., a 2-part epoxy resinor the like). Advantageously, fiber optic sensors configured inaccordance with embodiments of the present invention involve nopenetrations into the elongated tubular member to gain access tooperating condition information of a fluid therein. It is disclosedherein that the fiber-optic cable 108 can comprise a plurality ofinterconnected segments of cable, that the fiberoptic cable 108 cancomprise more than one optical fibers, and that the one or more opticalfibers of one or more segments of fiber-optic cable can be connected inan end-to-end manner to form a contiguous optical fiber structure.

The optical fiber 134 includes a light transmitting structure 136 (e.g.,a cladded core) and a polymeric coating 138 formed directly on the lighttransmitting structure 136. Polyimide and polyacrylate are examples ofsuch polymeric material. It is disclosed herein that the lighttransmitting structure 136 (e.g., the core or cladding thereof) cancontain Germania and/or Ebrium dopants for signal amplification and canbe made of a single mode of silica glass.

Advantageously, the applicants herein have discovered that, when theoptical fiber 134 has a polyimide coating, the optical fiber can bebonded directly to the optical fiber engagement portion 126 withoutremoval of such polyimide coating. In contrast, when the optical fiber134 has a polyacrylate coating, the polyacrylate coating is preferablyremoved from the light transmitting structure 136 of the optical fiber134 such that the light transmitting structure 136 of the optical fiber134 can be bonded directly to the optical fiber engagement portion 126.Without wishing to be bound by any particular theory, applicant believesthat one or more mechanical/physical properties of the polyimidematerial provide for negligible attenuation of strain and thermal eventsexhibited within the exterior surface of the elongated tubular member102 being communicated to the operating condition signal generatingportion 132 of the optical fiber 134. Examples of suchmechanical/physical properties of the polyimide material include, butare not limited to, modulus of elasticity, tensile strength, andcoefficient of friction.

The operating condition signal generating portion 132 of the opticalfiber 134 is within light transmitting structure 136. In preferredembodiments, the optical fiber 134 includes a plurality of operatingcondition signal generating portions spaced along its length, wherebyeach one of the fiber optic sensors 110-116 positioned along a length ofthe elongated tubular member 102 comprises a respective one of theoperating condition signal generating portions. Each operating conditionsignal generating portion 132 of the optical fiber 134 is configured tointeract with a respective different wavelength of light that istransmitted along the length of the optical fiber 134 within the lighttransmitting structure 136 (i.e., transmitted signal). Such interactiongenerates a corresponding signal (i.e., detected signal) thatcharacterizes a changes in the strain and/or temperature exhibitedwithin the operating condition signal generating portion 132 withrespect to baseline strain and/or temperature. By assessing the detectedsignal for a particular one of the fiber optic sensors 110-116,operating condition information of the elongated tubular member 102and/or a fluid therein at a location of the particular one of the fiberoptic sensors 110-116 can be determined such as by a suitably configuredalgorithm of a data acquisition system.

FIG. 7 shows an example of a detected signal in accordance withwavelength division multiplexing for a plurality of fiber optic sensorsthat each have an operating condition signal generating portion that isresponsive to a different wavelength of a transmitted signal (i.e., apulse of laser light of a known spectrum of wavelength). When theoperating condition signal generating portion of each fiber optic sensoris subjected to the transmitted signal, it produces a reflected signalhaving a power peak 140 at the responsive wavelength thereof for eachone of n fiber optic sensors. For example, a data acquisition systemconfigured in accordance with an embodiment of the present invention canclaim power greater than 20 dB within an interrogator thereof. Thewavelength of the reflected signal for a particular one of the fiberoptic sensors shifts higher or lower as a function of changes in lengthof the operating condition signal generating portion thereof due toexpansion and contraction resulting from changes in strain within theelongated tubular member, change in temperature of the elongated tubularmember and change in temperature of the operating condition signalgenerating portion of the optical fiber.

Through use of one or more fiber optic sensors that sense changes instrain within the elongated tubular member and at least one adjacentfiber optic sensor that monitors temperature at the location of theelongated tubular member where the strain-sensing fiber optic sensorsare located, one or more of the operating conditions can be derived.Such operating conditions include, but are not limited to, strain withina wall of an elongated tubular members, pressure within an interiorspace of the elongated tubular members, torsion applied to the elongatedtubular members, temperature of the wall or surface of the elongatedtubular members, temperature of a fluid within the interior space of theelongated tubular members, and flow confirmation of a fluid within theinterior space of the elongated tubular members.

Bragg grating, which are well-known to a person of ordinary skill in theart of optical fibers, is a preferred implementation of the operatingcondition signal generating portion 132 of the optical fiber 134.Wavelength for the Bragg gratings may range from about 1200 to about1700 nanometers with reflectively thereon being generally greater thanabout 10% and preferably greater than about 90%. Although Bragg gratingsare a preferred implementation of the operating condition signalgenerating portion 132, it is disclosed herein that otherimplementations of generating operating condition information are alsocontemplated herein. By way of example, such other that otherimplementations of generating operating condition information include,but are not limited to, distributed strain signal generating techniques,Sagano signal generating techniques, Micheloson signal generatingtechniques, and Fabry Pero signal generating techniques. It is alsodisclosed herein that electrical based sensors such as restive straingauges, accelerometers, and/or potentiometers may optionally be used(e.g., in combination with fiber optic sensors) for generating operatingcondition information. Furthermore, it is disclosed herein that opticaltime domain reflectometry methods are integrated into the Bragg gratingsor other similarly configured operating condition signal generatingportion for temperature monitoring.

FIG. 8 shows a preferred embodiment of the fiberoptic cable 108. Thefiberoptic cable 108 includes an outer jacket 150 formed over a tubulararmor layer 152 that is within a central passage 154 of the outerjacket. An end portion 156 of the outer jacket 150 and the tubular armorlayer 152 is secured within the sensor housing 117. A plurality ofoptical fibers 134 extend within the central passage 154. A length ofeach one of the optical fibers extends beyond the end portion 156 of theouter jacket 150 from within the central passage 154 and into the sensorhousing 117. For example, as discussed above in reference to FIGS. 2-6 ,one or more of the optical fibers 134 has operating condition signalgenerating portions 132 thereof attached to a respective tubular memberinterface body 118 for forming the optical fiber sensors 110-116 and,thus, extends beyond the end portion 156 of the outer jacket 150.

At least a portion of each one of the lengths of the optical fibers thatspans between the respective tubular member interface body 118 and theend portion 154 of the outer jacket 150 is disposed within a layer of aviscous material composition 158. The optical fibers 134 can each extendwithin a respective inner jacket 160. Where the optical fiber 135extends from the central passage 154 into the sensor housing 117 and iswithin the inner jacket 160, the viscous material composition 158 ispreferably within the inner jacket 160. When the optical fiber 134extends beyond an end portion of inner jacket 160 and/or there is noinner jacket (i.e., unjacketed optical fiber), a layer of the viscousmaterial composition 158 may be provided onto the optical fiber 134 suchas, for example, where it spans over the elongated tubular member 102.For example, as shown in FIG. 9 , a length of unjacketed optical fiber134 extends over the exterior surface of the elongated tubular member102 and is covered by a layer of protective material 161 (e.g., a layerof polymeric material such as polyurethane). In such case, the length ofunjacketed optical fiber 134 is preferably disposed within a layer ofthe viscous material composition 158.

In applications where the optical fiber is without protection of thetubular armor layer 152 and is subjected to pressure from use in asubsea environment, the applicant has discovered that disposing theoptical fiber 132 within a layer of viscous material composition isadvantageous. Without wishing to be bound to any specific theory,applicant believes that the layer of viscous material serves as ahydrostatic support that aids in mitigating non-uniform cross-sectionalcompression of the optical fiber and that aids in limiting theoccurrence of ‘microbeads’ resulting from the optical fiber being forcedagainst small-radius/sharp discontinuities with mating surfaces of thesensor housing 117 or elongated tubular member 102.

The viscous material composition preferably exhibits a relativelyuniform level of viscosity across a wide range of temperatures. Forexample, in a preferred embodiment, the viscous material composition isa grease that has an oil viscosity index of not less than about 120, atemperature range having an upper limit of at least about 200° C., andan oil viscosity of at least about 3.0 at 200° C. Examples of a grease(i.e., a viscous material composition) exhibiting such thermal viscositystability are commercially-available from E. I. du Pont de Nemours andCompany under the tradename and grades of KRYTOX GPL 205(H-1), KRYTOXGPL 206(H-1), KRYTOX GPL 207, KRYTOX GPL 216, KRYTOX GPL 217, KRYTOX GPL250AC, and KRYTOX GPL280AC.

Applicant has discovered that exposure of optical fibers to pressure ofa subsea environment can result in attenuation of a reflected signalwithin an optical fiber. It is theorized that such attenuation can bedue to cross-sectional distortion of the optical fiber such as, forexample, resulting from impingement of the optical fiber upondiscontinuities that create microbends in the optical fiber, fromcompression of the optical fiber against otherwise flat, sufficientlyrigid surfaces, and the like. The result is a reduction in signal powerand distortion of the signal profile, both of which can be detrimentalto accurate assessment of operating condition information. As discussedabove, the use of a viscous material composition can aid in mitigatingsuch attenuation. Optionally or additionally to use of such viscousmaterial composition, the operating condition signal generating portionsof an optical fiber (e.g., a light reflective grating thereof) can beadapted to at least partially mitigate signal attenuation caused byforce exerted on the optical fiber by the subsea environment. Forexample, the operating condition signal generating portions of theoptical fiber can be formed such that the light reflecting gratingthereof is configured to provide a designated Bragg condition exhibitedat an environmental pressure of one atmosphere when the optical fiber issubjected to a pressure exerted thereon by the subsea environment. Inpreferred embodiments, the environmental pressure corresponds to asubsea depth between about 1000 feet and about 5000 feet. Alternatively,or additionally, the operating condition signal generating portions ofthe optical fiber can be formed such that the light reflecting gratingis adapted to produce a signal having a peak amplitude that is at leastabout 50 dB and preferably not less than about 10 dB when in anenvironmental condition of 1 atmosphere.

As discussed above, use of fiber optic sensors in accordance withembodiments of the present invention within a subsea environment canresult in attenuation of a reflected signal within an optical fiber usedto communication signals to and from such fiber optic sensors. Thisattenuation is an example of environment-induced signal degradation. Tofurther mitigate such environment-induced signal degradation,apparatuses and systems configured in accordance with embodiments of thepresent invention can be calibrated to account for the environmentaleffects (e.g., a subsea environment).

In an embodiment of the present invention, such calibration comprises aplurality of steps. A step is performed for deploying an elongatedtubular member in a subsea environment. The elongated tubular member hasmounted thereon one or more fiber optic sensors that are each adaptedfor generating a respective form of operating condition information. Inthis respect, each one of the fiber optic sensors, which can beconfigured in the manner discussed above with respect to FIGS. 2-6 , isan operating condition sensor. A step is performed for causing anoperating condition information signal to be transmitted from the fiberoptic sensors to a data acquisition system (which can serve as acalibration apparatus) via one or more optical fibers of a fiberopticcable. As discussed above, the operating condition information signalcan be generated by an operating condition signal generating portion ofthe one or more optical fibers in response to being exposed to atransmitted signal of a given wavelength bandwidth.

In response to the data acquisition system receiving the operatingcondition information signal, a step is performed for determining anamount of attenuation of the operating condition information signal withrespect to a non-subsea environment. An environment comprising anatmosphere of air at a pressure of 1 atmosphere is an example of thenon-subsea environment. In response to determining the amount ofattenuation, a step is performed for calibrating signal processingfunctionality of the data acquisition system as a function of theattenuation of the operating condition information signal with respectto the non-subsea environment. For example, in a preferred embodiment,such calibration offsets at least a portion of the attenuation caused byforce exerted on the one or more optical fibers by pressure within thesubsea environment. Offsetting at least a portion of the attenuationcaused by force exerted on the one or more optical fibers by pressurewithin the subsea environment can include, for example, offsettingwavelength shift in a signal from the at least one operating conditionsensor within the subsea environment as a function of a baseline signalgenerated by the operating condition sensor at atmospheric (i.e.,baseline) conditions. Temperature and pressure are examples of suchatmospheric conditions. Such offsetting of the wavelength shift caninclude, for example, determining wavelength shift in at least one of anaxial direction of the elongated tubular member and a hoop direction ofthe elongated tubular member, offsetting the wavelength shift as afunction of a differential between a baseline temperature and atemperature of the subsea environment at a location of the operatingcondition sensor.

In a preferred embodiment of the present invention, the data acquisitionsystem is adapted to receive a signal comprising operating conditioninformation from a plurality of fiber optic sensors. The dataacquisition system, which can comprise an optical sensing module and/ora multiplexing unit with a time division multiplexing module, is adaptedto utilize WDM to derive information for a plurality of operatingconditions using information received from the plurality of fiber opticsensors. One example of such operating condition information is strainwithin the exterior wall of the elongated tubular member as a functionof a signal wavelength generated by the operating condition signalgenerating portion of a first one of the fiber optic sensors. Anotherexample of such operating condition information is pressure of a fluidwithin the central passage of the elongated tubular member as a functionof a signal wavelength generated by the operating condition signalgenerating portion of a second one of the fiber optic sensors. Yetanother example of such operating condition information is temperatureof the fluid within the central passage of the elongated tubular memberas a function of a signal wavelength generated by the operatingcondition signal generating portion of a third one of the fiber opticsensors.

Referring now to FIG. 10 , a multi-tubular member monitoring apparatus200 configured in accordance with an embodiment of the present inventionis shown. The multi-tubular member monitoring apparatus 200 includes aplurality of elongated tubular member 202 that are connected to asupport structure 204. A plurality of sensor housing assemblies 205a-205 n, 206 a-206 n are mounted in a spaced-apart arrangement along alength of a respective one of the elongated tubular members 202 a-202 n.The sensor housing assemblies 205 a-205 n, 206 a-206 n and the fiberoptic sensors thereof provide the same or similar functionality as thesensor housing assemblies and the fiber optic sensors discussed above inreference to FIGS. 1-6 .

The sensor housing assemblies 205 a-205 n of a first one of theelongated tubular members 202 a by a first optical cable 208 a and thesensor housing assemblies 206 a-206 n of an n-th one of the elongatedtubular members 202 n are connected to each other by an n-th opticalcable 208 b. The plurality of fiberoptic cables 1-n are connected to amultiplexing unit (MUX) 211 of a signal processor 213 for enablingsignals generated by the sensor housing assemblies 205 a-205 n, 206a-206 n to be provided to the signal processor 213. The MUX 211 isconnected to an optical sensing module 209 and includes a Time DivisionMultiplexing (TDM) module 215. The optical sensing module 209 of FIG. 10, as well as the optical sensing module 107 of FIG. 1 , can providesignal processing functionality and calibration functionality, asdiscussed above.

Referring to FIG. 11 , the MUX 211 includes a plurality of optical fiberinterfaces 217 a-217 n each having a downstream facing port 219 and anupstream facing port 221. The upstream facing port 219 of each one ofthe optical fiber interfaces 217 a-217 n is connectable to each otherone of the upstream facing ports 219 for allowing each end of each oneof a plurality of optical fibers 223 a-223 n of one or more fiberopticcables (e.g., the fiberoptic cables 208 a-208 n) to be operablyconnected to the downstream facing port of a respective one of theoptical fiber interfaces 217 a-217 n such that at least two of theoptical fibers are connected to each in a series fashion to form acontiguous optical fiber structure having opposing ends. For example, asshown in FIG. 11 , the contiguous optical fiber structure comprises theplurality of optical fibers 223 a-223 n. The upstream facing portconnected to an end of the contiguous optical fiber structure isconnected to a first signaling port of the optical sensing module 209via a first signaling port 225 a of the MUX 211 for enabling sensor datagenerated within the contiguous optical fiber structure to be providedfrom the MUX 211 to the optical sensing module 209.

As shown in FIG. 11 , signaling is performed in a conventional manner,which is via a first one of the ends of the contiguous optical fiberstructure. Advantageously, however, the MUX 211 and, optionally, the TDMmodule 215 of the MUX 211 also allow multiple configurations of signalbeing provided from the first and second fiber optic cables 208, 209 tothe optical sensing module 209 in the case where one or morediscontinuities occur within the contiguous optical fiber structure.

As shown in FIG. 12 , when a discontinuity 227 occur within a particularone or more of the one optical fibers 223 a-223 n of the contiguousoptical fiber structure (e.g., optical fiber 223 b), the MUX 211 may beadapted to implement an operating condition signal to be provided atboth of the opposing ends of the contiguous optical fiber structure andmonitoring a respective operating condition signal at both of the endsof the contiguous optical fiber structure. For example, in a preferredimplementation of the operating condition signal being provided at bothof the opposing ends of the contiguous optical fiber structure andmonitoring the respective operating condition signal at both of suchends, a first operating condition signal provided via at a first end ofthe contiguous optical fiber structure and a second operating conditionsignal provided via at a second end of the contiguous optical fiberstructure is monitored by the optical sensing module 209. The TDM module215 of the MUX 211 can be used for enabling monitoring of the firstoperating condition signal provided via at the first end of thecontiguous optical fiber structure and the second operating conditionsignal provided via at the second end of the contiguous optical fiberstructure via a single signaling port of the optical sensing module 209.

Alternatively, as shown in FIG. 13 , when the discontinuity 227 occurswithin the particular one or more of the optical fibers 223 a-223 n ofthe contiguous optical fiber structure (e.g., optical fiber 223 b), theMUX 211 may be adapted to implement excluding (e.g., bypass) theparticular one or more of the optical fibers 223 a-223 n from within thecontiguous optical fiber structure to create a reconfigured version ofthe contiguous optical fiber structure and continuing to monitor theoperating condition signal provided at the first end of the contiguousoptical fiber structure (i.e., via the first signaling port 225 a of theMUX). It is disclosed herein that the abovementioned functionalities ofthe MUX 211 may be implemented manually and/or in an automated mannerusing optical switches and/or physical couplings. For example, in apreferred implementation of the particular one or more of the opticalfibers 223 a-223 n being excluded from within the contiguous opticalfiber structure, detaching the particular one or more of the opticalfibers 223 a-223 n can include detaching first and second ends of theparticular one or more of the optical fibers 223 a-223 n from acorresponding end of adjacent ones of the optical fibers 223 a-223 n andconnecting together the corresponding ends of the adjacent ones ofoptical fibers 223 a-223 n.

It is disclosed herein that the above-mentioned MUX functionalities canbe implemented in response to a signal assessment process. The signalassessment process may begin with monitoring an operating conditionsignal provided at one of the ends of the contiguous optical fiberstructure to determine operating condition information generated by theoperating condition sensors thereof, followed by detecting loss ofoperating condition information corresponding to at least one of theindividual lengths of optical fiber. In response to detecting the lossof operating condition information, the signal assessment process causesreconfiguration of the monitoring of the operating condition signal inaccordance with at least one of the above-mentioned MUX functionalities

FIGS. 14-17 shown a pipeline system having aspects configured inaccordance with one or more embodiments of the present invention. Asshown in FIG. 14 , a typical pipeline 310 is positioned for deploymentin a subsea environment. As discussed above, the fiber optic sensors areattached directly to the outer wall 312 by an epoxy 14, as shown in FIG.15 . The data collected by a sensor array is then conducted to a fiberbreakout assembly or collector 318 via the fiber optic cable 316, whichis attached to the sensors in the array, as disclosed in FIG. 16 . Thecollected data is then conducted to a topside control room (not shown)via the conductor 320. An alternative collector 322 is shown in FIG. 17, wherein a plurality of sensor array cables 316 may be connected to asingle collector 322 for transmitting the collected data to the topsidecontrol room via cable 320.

The cabling, connectors, breakout assemblies and support hardware aredesigned to provide ruggedness during installation and provideattenuation free light transfer. The system is designed for long servicelife and has measure incorporated to minimize any light transmittalissues such as fiber darkening from hydrogen infusion. Since there arevarious local measurement locations along the pipeline fiber breakoutassemblies incorporated into the invention. Additionally, there is acombination of fiber optic measurements that are integrated into thesystem.

Preferably, the system contains a multiple of fiber Bragg grating arraysdeployed subsea along the pipeline. All tubing is stainless steel. Wheredesired, Kevlar jackets may be employed.

The time of flight for the light signal is incorporated in the topsidemonitoring system in the control room.

Attenuation mitigation is used by the use of a pressure balancingmaterial applied to the fiber optic strands in the fiber optic cables.Preferably, the fiber optic cables are coated with a polyurethane,nylon, or polyethylene coating. Polyurethane and epoxy housings are usedon top of the sensor stations.

The subsea sensors use hoop displacement of the pipeline the pipeline todetermine product pressure from the exterior of the pipeline. Nopenetrations into the pipeline are necessary to gain access to the flowstream measurements. The connections are designed with a small angledferrule to minimize back reflections.

Fiber bundles are multi-fused (more than one fusion splice) in eachbreakout assembly to reduce space requirements.

Although the invention has been described with reference to severalexemplary embodiments, it is understood that the words that have beenused are words of description and illustration, rather than words oflimitation. Changes may be made within the purview of the appendedclaims, as presently stated and as amended, without departing from thescope and spirit of the invention in all its aspects. Although theinvention has been described with reference to particular means,materials and embodiments, the invention is not intended to be limitedto the particulars disclosed; rather, the invention extends to allfunctionally equivalent technologies, structures, methods and uses suchas are within the scope of the appended claims.

What is claimed is:
 1. An apparatus for sensing operating conditioninformation from an elongated tubular member, comprising: a plurality oftubular member interface bodies each including a tubular memberengagement portion and an optical fiber engagement portion; a pluralityof optical fibers each having a first end and a second end, wherein twoor more of the optical fibers have at least one operating conditionsignal generating portion between the first and second ends thereof andwherein the at least one operating condition signal generating portionof said two or more of the optical fibers is attached along a length ofthe optical fiber engagement portion of a respective one of the tubularmember interface bodies to thereby form a plurality of operatingcondition sensors connected to the elongated tubular member; an opticalsensing module having at least one signaling port; and a multiplexingunit including a plurality of optical fiber interfaces each having adownstream facing port and an upstream facing port, wherein the upstreamfacing port of each one of the optical fiber interfaces is connectableto each other one of the upstream facing ports, wherein each end of eachone of the optical fibers is operably connected to the downstream facingport of a respective one of the optical fiber interfaces, wherein theupstream facing ports are connected to each other such that at least twoof the optical fibers are connected in a series fashion to form acontiguous optical fiber structure having opposing ends and wherein theupstream facing port connected to an end of the contiguous optical fiberstructure is connected to the at least one signaling port of the opticalsensing module for enabling sensor data generated within the contiguousoptical fiber structure to be provided from the multiplexing unit to theoptical sensing module.
 2. The apparatus of claim 1 wherein: thecontiguous optical fiber structure includes a plurality of operatingcondition signal generating portions that each generate operatingcondition information when exposed to light provided thereto by theoptical sensing module; the optical sensing module includes a signalcontroller, a first signaling port and a second signaling port; thesignal controller is connected to the first signaling port and to thesecond signaling port; the upstream facing port connected to a first oneof the opposing ends of the contiguous optical fiber structure isconnected to the first signaling port; the upstream facing portconnected to a second one of the opposing ends of the contiguous opticalfiber structure is connected to the second signaling port; and thesignal controller is configured to automatically transition fromproviding signaling functionality at only the first signaling port toprovide signaling functionality at both the first and second signalingports after the optical sensing module determines that an operatingcondition signal received at the optical sensing module includesoperating condition information from less than all of the optical fibersof the contiguous optical fiber structure.
 3. The apparatus of claim 2wherein providing signaling functionality at both the first and secondsignaling ports includes implementing time division multiplexing at thefirst and second signaling ports.
 4. The apparatus of claim 1 wherein:the optical sensing module includes a time division multiplexor; thetime division multiplexor includes a first signaling port and a secondsignaling port; the upstream facing port connected to a first one of theopposing ends of the contiguous optical fiber structure is connected tothe first signaling port; the upstream facing port connected to a secondone of the opposing ends of the contiguous optical fiber structure isconnected to the second signaling port; and the time divisionmultiplexor is configured to implement time division multiplexingfunctionality at the first and second signaling ports after the opticalsensing module determines that an operating condition signal received atthe first signaling port includes operating condition information fromless than all of the optical fibers of the contiguous optical fiberstructure.
 5. The apparatus of claim 1 wherein: the at least oneoperating condition signal generating portion of each one of two or moreoptical fibers is located within a subsea environment; the opticalsensing module and the multiplexing unit are located at a locationexternal to the subsea environment; and at least a portion of each oneof the optical fibers is configured for limiting signal attenuationresulting from pressure exerted thereon by the subsea environment. 6.The apparatus of claim 5 wherein: the at least one operating conditionsignal generating portion of each one of the optical fibers is locatedwithin the subsea environment; a fiber core of each one of the opticalfibers at the operating condition signal generating portion thereofincludes a light reflective grating therein; and the light reflectinggrating is adapted to at least partially mitigate signal attenuationcaused by force exerted on the optical fiber by the environmentalpressure within the subsea environment.
 7. The apparatus of claim 5wherein: each one of the optical fibers includes a light transmittingstructure and a layer of polyimide material covering the lighttransmitting structure; the layer of polyimide material is applieddirectly onto the light transmitting structure; and the layer ofpolyimide material at the operating condition signal generating portionof the optical fiber is bonded directly to the respective one of thetubular member interface bodies.
 8. The apparatus of claim 5 wherein:said optical fibers extend within an internal passage of a fiberopticcable; a length of each one of said optical fibers within the subseaenvironment extends from within the outer jacket of the fiberopticcable; and at least a portion of each one of the lengths of said opticalfibers that extends from within the outer jacket is disposed within alayer of a viscous material composition.
 9. The apparatus of claim 1wherein at least one of the optical sensing module and the multiplexingunit is adapted for: monitoring an operating condition signal providedat one of opposing ends of the contiguous optical fiber structure todetermine operating condition information generated by the plurality ofoperating condition sensors; detecting, via the operating conditionsignal, loss of operating condition information corresponding to atleast one of the optical fibers; and in response to detecting the lossof operating condition information, reconfiguring monitoring of theoperating condition signal, wherein reconfiguring said monitoringincludes one of: causing an operating condition signal to be provided atboth of said opposing ends of the contiguous optical fiber structure andmonitoring a respective operating condition signal at both of said endsof the contiguous optical fiber structure; and excluding the at leastone of the optical fibers from within the contiguous optical fiberstructure to create a reconfigured version of the contiguous opticalfiber structure and continuing to monitor the operating condition signalprovided at said one of the opposing ends of the contiguous opticalfiber structure.
 10. The apparatus of claim 9 wherein causing theoperating condition signal to be provided at both of said opposing endsof the contiguous optical fiber structure and monitoring the respectiveoperating condition signal at both of said ends of the contiguousoptical fiber structure includes: monitoring a first operating conditionsignal provided via at a first end of the contiguous optical fiberstructure that is connected to a first signaling port of the opticalsensing module; and monitoring a second operating condition signalprovided via at a second end of the contiguous optical fiber structurethat is connected to a second signaling port of the optical sensingmodule.
 11. The apparatus of claim 10 wherein monitoring the first andsecond operating condition signals is performed using time divisionmultiplexing at the first and second signaling ports.
 12. The apparatusof claim 9 wherein excluding the at least one of the individual lengthsof optical fiber from within the contiguous optical fiber structureincludes: detaching first and second ends of the at least one of theoptical fibers from a corresponding end of adjacent ones of the opticalfibers; and connecting together the corresponding ends of the adjacentones of the optical fibers.
 13. The apparatus of claim 12 whereindetaching the first and second ends of the at least one of the opticalfibers and connecting together the corresponding ends of the adjacentones of the optical fibers is performed within a multiplexing unitwithin which at least one of the ends of a particular one of the opticalfibers is attached to an end of another one of the optical fibers toform the contiguous optical fiber structure.